In the manufacture of components, such as nickel base superalloy turbine blades and vanes, for gas turbine engines, directional solidification investment casting techniques have been employed in the past to produce single crystal or columnar grain castings having improved mechanical properties at high temperatures encountered in the turbine section of the engine.
In the manufacture of turbine blades and vanes for modern, high thrust gas turbine engines, there has been a continuing demand by gas turbine manufacturers for internally cooled blades and vanes having complex, internal cooling passages including such features as pedestals, turbulators, and turning vanes in the passages to control the flow of air through the passages in a manner to provide desired cooling of the blade or vane. These small cast internal surface features typically are formed by including a complex ceramic core in the mold cavity in which the melt is cast. The presence of the complex core having small dimensioned surface features to form pedestals, turbulators, turning vanes or other internal surface features renders filling of the mold cavity about the core with melt more difficult and more prone to inconsistency. Wettable ceramics and increased metallostatic head on the mold have been used in an attempt to improve mold filling and reduce localized voids in such situations, but these are costly and may be restricted by physical size of the casting apparatus.
It is an object of the present invention to provide a method of casting a melt in a mold in a manner that improves filling of one or more mold cavities with the melt.
It is another object of the invention to provide a method of casting a melt in a mold in a manner that improves filling about a ceramic core disposed in a mold cavity to form cast internal surface features, especially fine or small dimensioned surface features, such as the pedestals, turbulators, and turning vanes described hereabove for internally cooled turbine blades and vanes.
It is another object of the invention to decrease the level of internal porosity formed during solidification of the melt.
It is still another object of the invention to provide a method of casting a melt in an evacuated mold-followed by rapid application of pressure on the melt cast in the mold in a manner that improves filling about a ceramic core disposed therein to form cast internal surface features, such as fine or small dimensioned cast internal surface features.